By the time of the Napoleonic wars, an infantrybattalion usually had two majors, designated the "senior major" and the "junior major". The senior major effectively acted as second-in-command and the majors often commanded detachments of two or more companies split from the main body. The second-in-command of a battalion or regiment is still a major.

1856 to 1867 major's collar rank insignia

1867 to 1880 major's collar rank insignia

1881 to 1902 major's shoulder rank insignia

During World War I, majors wore the following cuff badges:

1902 to 1920 major's sleeve rank insignia (general pattern)

1902 to 1920 major's sleeve rank insignia (Scottish pattern)

During World War I, some officers took to wearing similar jackets to the men, with the rank badges on the shoulder, as the cuff badges made them conspicuous to snipers. This practice was frowned on outside the trenches but was given official sanction in 1917 as an alternative, being made permanent in 1920 when the cuff badges were abolished.

From 1 April 1918 to 31 July 1919, the Royal Air Force maintained the rank of major. It was superseded by the rank of squadron leader on the following day.

By World War I, majors were often commanding independent companies, squadrons and batteries, but those that were organically part of a regiment or battalion were still usually commanded by captains. After World War II, major became the usual rank held by officers commanding all companies, squadrons and batteries, and remains so today.